(1) Field of the Invention
The present invention relates to a ceramic honeycomb structural body, a method of manufacturing the same, an extrusion die therefor, and a rotary regenerator type ceramic heat exchanger utilizing such a ceramic honeycomb structural body as a main component. More specifically, the invention relates to a ceramic honeycomb structural body which is suitable for use in a rotary regenerator type ceramic heat exchanger for a gas turbine including a ceramic heat exchanger for the automobiles as a preferred embodiment, a method of manufacturing the same, and a die of extruding the same, and a rotary regenerator type ceramic honeycomb type heat exchanger.
The ceramic honeycomb structural body used herein means a ceramic structural body having a plurality of cells divided by partition walls.
(2) Description of the Prior Art
Heretofore, there have been known, as the ceramic honeycomb structural body, that obtained by a corrugation molding method disclosed in Japanese Patent Publication No. 48(1973)-22,964, that obtained by an embossing molding method as disclosed in U.S. Pat. No. 3,755,204, and that obtained by an extrusion molding method as disclosed in Japanese Patent Laid-Open No. 55(1980)-46,338.
It is reported, however, that honeycomb structural bodies according to the corrugation molding method and the embossing molding method unfavorably have a large pressure drop (.DELTA.P) and a large wall surface friction factor (friction factor) (F) because the profile of the cells are ununiform and the surfaces of the cells are not smooth, and particularly, since the honeycomb structural body according to the corrugation molding method has the cells with a sine triangular shape in section, the corner portions thereof are acute, and the ratio of basic heat transfer (Colburn number) (J) is poor, so that the heat exchange efficiency is small.
On the other hand, gas turbine rotary regenerator type ceramic heat exchangers for gas turbines including the rotary regeneration type ceramic heat exchanger for automobiles as a preferred embodiment thereof, has demanded ceramic honeycomb heat exchangers having excellent heat exchange efficiency, while being compact with high performances, since they need to be placed in a limited space. The heat exchange efficiency of the ceramic heat exchanger is broken down into a heat exchange efficiency of a unit cell and the heat exchange efficiency as the whole heat exchanger. The heat exchange efficiency of the unit cell can be evaluated by the overall fin efficiency (J/F), in which J and F are represented by a function of the Reynolds number respectively. The heat exchange efficiency of the whole heat exchanger is represented by the exchanger heat transfer effectiveness (.epsilon.) and the pressure drop (.DELTA.P), and is represented by a function of the flow rate of a fluid per unit area of the heat exchanger.
The ceramic heat exchanger obtained by extrusion molding has the merits that since it has a uniform shape and smooth cell surfaces, the pressure drop and the friction factor are small, and the Colburn number is large, the overall fin efficiency is large as compared with the other manufacturing methods. In order to obtain a ceramic heat exchanger having an excellent heat exchange efficiency, it is necessary to enhance the exchanger heat transfer effectiveness by selecting a cell structure with a large overall fin efficiency and densifying the cells, and reduce the pressure drop of the heat exchanger.